This page describes the ''work-in-progress'' design of an SDR based receiver station for the 5.8 GHz band, originally created for tracking the [http://www.unisec.jp/unitec-1/en/top.html UNITEC-1] spacecraft on its interplanetary journey to Venus.

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This page describes the design of a software defined radio receiver station for the 5.6-5.9 GHz band, originally created for tracking the [http://www.unisec.jp/unitec-1/en/top.html UNITEC-1] spacecraft on its interplanetary journey to Venus.

Event logbook is available on the [[Talk:C-band_Receiver_Station#Logbook|talk page]].

Event logbook is available on the [[Talk:C-band_Receiver_Station#Logbook|talk page]].

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[[Image:FuncOverviewSketch.001.png|800px]]

[[Image:FuncOverviewSketch.001.png|800px]]

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== Link Budget for UNITEC-1 ==

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== Link Budget ==

=== Summary ===

=== Summary ===

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The detailed link budget calculations are available here: [[Image:UNITEC-LinkBudget.ods]].

# An optimistic estimate suggests that we should be able to receive UNITEC-1 up to 10-15 million km distance.

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# There is plenty of margin in the beginning and we can use a low gain antenna for initial acquisition. The IKEA dish has ~25 dBi gain and it could be used up to 1 million km where after the trajectory is hopefully well known.

== Antenna ==

== Antenna ==

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=== Parabolic Dish ===

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=== Small 90cm Dish ===

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The small 90cm dish is used to to find UNITEC-1 in the beginning. We created a small helical feed antenna with two turns.

We have about 40 meters of H1000-class (TBC) cable running from the Dish to the control room and using 1.4-1.7 GHz as first IF would result in too much loss. Therefore, we chose the 5659 PRO version which has output in the 400-700 MHz range where the cable loss is limited to 6 dB (TBC).

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We have about 40 meters of H1000-class cable running from the Dish to the control room and using 1.4-1.7 GHz as first IF would result in too much loss. Therefore, we chose the 5659 PRO version which has output in the 400-700 MHz range where the cable loss is limited to 6 dB (TBC).

The LNC is supplied via the coax cable. DC viltage is injected into the coax using [[Receiving_LRO_and_LCROSS#Bias-T|KU BT 271 N]] bias-T from Kuhne. We also had something called MSTTR001 from Snec but that is believed to work up to 100 mA, while the LNC typically requires 180 mA.

The LNC is supplied via the coax cable. DC viltage is injected into the coax using [[Receiving_LRO_and_LCROSS#Bias-T|KU BT 271 N]] bias-T from Kuhne. We also had something called MSTTR001 from Snec but that is believed to work up to 100 mA, while the LNC typically requires 180 mA.

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European EME Contest on 5.8 GHz. We missed this opportunity because the antenna was not finished.

European EME Contest on 5.8 GHz. We missed this opportunity because the antenna was not finished.

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=== 2010.05.18 ===

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Tested small 90cm dish with home made helical feed using OZ7IGY, see [http://www.oz9aec.net/index.php/gnu-radio/gnu-radio-blog/336-58-ghz-helical-feed-for-the-90cm-dish blog post].

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=== 2010.05.21 ===

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Since we couldn't receive UNITEC-1 using the 90cm dish we decided to move the LNC over to the 7 meter dish. Once done we tested the receiver system on 5.7 GHz using OZ7IGY. This was actually the first time we tested the complete receiver chain as depicted in the [[#System Overview|System Overview]] diagram.

UNITEC-1 is the first interplanetary spacecraft built by university students. It will be transmitting telemetry using OOSK at 1 bps in the 5.7 GHz amateur radio band using a 10W RF into a pair of patch antennas. UNITEC-1 operators need the help of the global amateur radio community for tracking their spacecraft during its journey to Venus[1]. Antenna pointing and Doppler shift measurements will be used for estimating the interplanetary trajectory of the craft.

TBDs and TBCs

Conclusions

An optimistic estimate suggests that we should be able to receive UNITEC-1 up to 10-15 million km distance.

There is plenty of margin in the beginning and we can use a low gain antenna for initial acquisition. The IKEA dish has ~25 dBi gain and it could be used up to 1 million km where after the trajectory is hopefully well known.

Antenna

Small 90cm Dish

The small 90cm dish is used to to find UNITEC-1 in the beginning. We created a small helical feed antenna with two turns.

We have about 40 meters of H1000-class cable running from the Dish to the control room and using 1.4-1.7 GHz as first IF would result in too much loss. Therefore, we chose the 5659 PRO version which has output in the 400-700 MHz range where the cable loss is limited to 6 dB (TBC).

The LNC is supplied via the coax cable. DC viltage is injected into the coax using KU BT 271 N bias-T from Kuhne. We also had something called MSTTR001 from Snec but that is believed to work up to 100 mA, while the LNC typically requires 180 mA.

Receiver

The USRP equipped with a WBX transceiver board and the TVRX receiver.

The receiver is a software defined radio and has two parts:

The hardware part — Converts the 400-700 MHz IF to baseband and sends it to a computer

The software part — Takes the baseband data from the hardware and performs filtering and demodulation in software

Receiver Hardware

The receiver hardware is based on the Universal Software Radio Peripheral (USRP) equipped with a WBX transceiver board. On the receiver side, it is a direct conversion software defined radio architecture where the RF is converted to baseband using a quadrature demodulator (ADL5387), digitized using 12 bit A/D converters (AD9862) and down-sampled using an FPGA. The resulting digital data is 16 bit signed I/Q that is sent to the host computer via USB2 interface.

The USRP Architecture

The USRP can host 2 receivers and 2 transmitters that can work at the same time sharing a total bandwidth of 8 MHz. Note that the ADCs are clocked at 64 MHz but the effective bandwidth is limited by the USB 2.0 interface to the host computer.

When we take all the protocol and other overhead away, USB 2.0 gives us 32 Mbytes/sec data rate. The USRP1 uses complex 16 bit signed integers (4 bytes/sample) and therefore we get 8 Msps. Since we use complex processing this gives a maximum effective total bandwidth of 8 MHz.

The WBX Receiver

The WBX is a full duplex transceiver board covering 50 MHz – 2.2 GHz. For this project we are only concerned about the receiver.

A block diagram of the WBX receiver is shown below. The detailed schematics are available from Ettus Research website.

Two HMC174MS8 GaAs MMIC T/R switches are used to configure the connection between antenna connectors and receiver/transmitter. We will use the RX2 input so that we only have one switch in the loop (estimated 0.5 dB improvement).

ADA4937-2 low distortion differential ADC driver brings the signal up to level suitable for the ADC. The ADC full scale is 2 Vpp / 50Ω differential but there is also a 20dB PGA reducing the required input level to 0.2 Vpp.

The USRP FPGA

The FPGA contains the digital down-converter that decimates the data to fit within the 8 MHz we can transfer over the USB. Actually, the decimation is variable between 8 and 256 allowing for bandwidth as low as 250 kHz (64MHz/256). The decimation factor is distributed between a four stage decimating Cascaded integrator-comb filter and a 31 tap halfband filter that decimates by 2.

Note that the FPGA design also includes a mixer and an oscillator (NCO) which allows the use of intermediate frequency input instead of baseband. This is very useful when we use an RF front end like the TVRX which outputs a 6 MHz wide spectrum centered around 5.75 MHz. Other RF boards output baseband signal centered around 0 Hz; however, the NCO is also useful for these board. The local oscillators on the RF boards have a limited resolution that does not always (read rarely) allows tuning to the exact frequency requested by the user. Using the NCO we can compensate for this difference. Fortunately, this is done automatically by the USRP and/or the GNU Radio driver and we don't have to worry about it.

2010.04.13

New session where we attempted reception of OZ7IGY. Tests were successful even though we only received a reflection and not the direct signal from OZ7IGY. Details are in blog post.

2010.04.24

European EME Contest on 5.8 GHz. We missed this opportunity because the antenna was not finished.

2010.05.18

Tested small 90cm dish with home made helical feed using OZ7IGY, see blog post.

2010.05.21

Since we couldn't receive UNITEC-1 using the 90cm dish we decided to move the LNC over to the 7 meter dish. Once done we tested the receiver system on 5.7 GHz using OZ7IGY. This was actually the first time we tested the complete receiver chain as depicted in the System Overview diagram.